Why is data stored on a NAND chip irretrievable if cracked?

Question

All data recovery companies, regardless of skill, unanimously say that if the memory chip of a device has just a hair line crack, data recovery is impossible. Not unlikely, not expensive, but impossible. One company even stated that even the FBI can't retrieve the data. Is this true?

Why is this? I find it hard to believe if just a tiny section of an extremely common chip has a tiny crack, all of the data is completely gone.

I would have thought some talented person somewhere would be able to patch up the area of the chip and get some of the data back...

Is it something to do with the charge? I know flash memory uses transistors to store its ones and zeroes in the form of an electrical charge. If the chip is cracked, do the transistors "short-out", turning them all to zeroes, something like that? Is the data gone rather than irretrievable?

All I want to get are some awesome holiday videos back. Thought they were gone for good, then I learned about data retrieval, thought I had a good chance of getting them back and then I realised there's not really a chance at all if the memory chip is cracked.

How much would retrieval be? Hundreds? Or thousands? A million, as RedGrittyBrick says? If were to hold onto the memory card, in a few years do you reckon the price of such an advanced retrieval could come down? Or is this just being unrealistic?

We're talking about a 256mb sd card here.

I suppose technologies are moving away from SD cards and more to integrated memory and then goodness knows what else...atomic memory, DNA memory..You don't see people coming out with new advanced procedures regarding cassette tapes today, do you? Should I just bite the bullet and give up?

Also, I'm not even a hobbyist in this field, however I am interested in general by how things work so if someone could explain simply the problem I would appreciate it.

Answer 1

All I want to get are some awesome holiday pictures back.

Lets be frank. They are not worth $1M to you are they. For that sort of money you could go on that holiday again a few times and recapture the same photos or something equally awesome.

I would have thought some talented person somewhere would be able to patch up the area of the chip

The technologies used to manufacture flash memory do not lend themselves to repairing cracked ICs. The manufacturing approach is to simply test and discard defective dies. There is no established technology capable of making repairs.

A silicon fab capable of manufacturing ICs costs $1bn. Any plant capable of repairing ICs is likely to be similarly expensive - it would need high volume usage to be economical. There just isn't that demand, most people probably find it cheaper and easier to copy photos onto a few $50 hard disks than to hope for sci-fi movie tech to rescue them.

Your talented person might need millions of dollars worth of equipment, a university-grade set of research labs, a large team of postgraduates and years or decades of funding.

and get some of the data back.

Some of the data may still be present in undamaged parts of the chip but conventional retrieval is likely to be completely dependent on damaged portions.

We're talking about a 256mb sd card here.

Imagine examining 2,000,000,000 individual grains of sand one at a time under a microscope. That's the scale of task involved. Grains of sand are much bigger than transistors of course. Transistors on flash-memory chips are far too small to see.

in a few years do you reckon the price of such an advanced retrieval could come down?

In a few hundred years?

Should I just bite the bullet and give up?

Unless you are a billionaire with nothing much else to do who can fit this into some kind of bigger plan.

Answer 2

Let's think about the scale of the problem. Silicon chips are very fragile, as are the very thin bonding wires that go from the chip to the pins/pads. They are also susceptible to environmental damage. That's why dies and wafers are handled in clean rooms, etc.

We take low cost, reliable, environmentally sealed chip packaging for granted. It actually took quite a long time to develop to this stage. I mention this because I think it helps to understand that an IC is not just a plastic box around an indestructible die. Chip packing is a big deal and provides a lot of protection that the die really needs.

Answer 3

I think this is a question of capability - as answers above indicate, a cracked IC is likely to be electrically non-functional and possibly damaged if it was powered up at the time.

Many data-recovery outfits rely on clever(ish) software - that is, the device still works and you just have to access it at a very low-level to tease the data out and re-assemble it into something usable.

However, there are stages below that depending on how much time and money you're wiling to throw at the problem.

There was a story on Hackaday a while back where a guy actually de-capped a gameboy ROM and read the bits out using a microscope and some image-processing software to read the set/unset bits. Now, that's not too taxing for an old ROM chip as there's a physical change visible, albeit requiring significant effort & a steady hand. For a modern flash chip, the density is insane and the change may be invisible. However, I would say it's not impossible, just incredibly hard. With suitable technology you could probe the chip die directly and probably read out some of the data, depending on the damage.

In all likelihood, this work is beyond most people's scope/budget. I'd guess that the FBI or MiB or whoever could do this if they felt it worthwhile, but I'd also guess that they wouldn't broadcast the fact to joe public, or that it may be classified or related to other classified capabilities.

Edit to add: An analogy might be a broken record; You can clean up the sound from a scratched record with clever processing, but a broken one can't be played on a turntable. It doesn't mean you couldn't get the data off, just that it's become a lot harder.

Answer 4

The chip is a large casing for a silicon wafer a few mm wide and the width of a few hairs. A crack means flexing pressure and direct damage to the bonding wires at best, or to the microscopically small traces and junctions on the wafer.

Think of it like a sheet of ice. The slightest bend and CRACK. Silicon Wafers are not designed for structural integrity under pressure.

While bond wires are possible to repair, damage to the wafer is practically impossible.

Answer 5

The data may well still be there, the problem is that there is no (reasonable) way to get an electrical signal into or out of the data cells. When you crack a chip you are cracking wires. The minimum feature size in many chips made these days is around 20nm=200 Angstroms. I suppose that if you (a) had an electron microscope, (b) knew exactly how the manufacturer had laid out the chip (what every wire means, and what signals need to be sent where to get the data), and (c) had some kind of electron microscope based soldering iron or micro-manipulator with a tip just a few atoms wide, you could laboriously and painstakingly repair all those broken connections.

But, while data recovery companies (the super duper ones) might have electron microscopes, I doubt they have either (b) any access to the manufacturer's layout or (c) a micromanipulator that could actually be used to do the repair. Also, we're talking about potentially needing to repair thousands of connections, so even if someone were able to do it, they'd probably charge tens or hundreds of thousands of dollars.

Answer 6

The problem is not so much that the flash memory cells (bits) are damaged so much as the addressing and readout electronics are damaged. Flash memory is not like a record, tape, CD, etc. where the read/write head is separate from the recording medium. In that case, damage to the medium just results in some unreadable data, the rest can still be read just fine by positioning the read/write head over the 'good' portion of the medium. However, flash memory has the 'read/write head' (row and column select wires, decoders, sense amplifiers, etc) integrated on the same piece of silicon as the recording medium (floating gate transistors). As a result, when the die is damaged, huge sections become completely inaccessible due to the damaged wiring. This wiring is built up on many layers on the chip and it is extremely small. And there are millions and millions of wires. If the die is snapped in half, it would take months inside of very expensive equipment to attempt to repair the damage, complicated by trying to not disturb the data. Note that flash memory is directly descended from UV eraseable EPROM, so once the chip is decapped, it must not be exposed to UV light (sunlight, etc.) so the data is preserved. Also, certain techniques used to examine and repair the chip such as ion beam etching could also disturb the stored charge in the floating gates.

Answer 7

It is theoretically possible on low density <500MB chips, IIRC there was a case fairly recently where someone had stored RSA keys on an old 32MB pendrive and snapped it in half as their front door was bashed in. To decrypt the files would have taken close to a decade but fortunately it was possible to recover enough consistent data from the paper fragments and the two 16MB slightly damaged Flash chips to make an educated guess at the 1024 bit key and with the combined brute force method they retrieved the files in less than a month.

I can only assume that the reason for storing them on such an old drive was data integrity, had that been a more modern multi-GB drive there would have been no hope of recovery ever.